Review Apps

Review apps create a temporary, fully working environment for each pull request. Reviewers click a real link, exercise real code, and see real config — instead of trying to imagine what your branch does from a diff.

What happens

When a pull request opens against a connected repository:

1. Watasu creates a preview app
2. Provisions the add-ons declared in app.json
3. Deploys the PR’s source
4. (Optionally) runs scripts.postdeploy to seed data, run migrations, etc.

When the pull request closes or merges:

1. (Optionally) runs scripts.pr-predestroy for any cleanup
2. Tears down the preview app and its add-ons

Requirement: app.json

app.json is required for review apps. It’s how Watasu knows what to provision and configure for each PR.

A minimal app.json for review apps:

{
  "env": {
    "RAILS_ENV": { "value": "production" }
  },
  "addons": [
    "postgresql:hobby-0",
    "valkey:hobby-0"
  ],
  "formation": {
    "web": { "quantity": 1, "size": "standard-1x" }
  },
  "scripts": {
    "postdeploy":   "bundle exec rails db:prepare && bundle exec rails db:seed",
    "pr-predestroy": "bundle exec rails app:cleanup"
  }
}

For the full schema, see Reference → app.json Schema.

Good uses

• design and product reviews on real UI
• migration and seed-data validation against real databases
• integration tests against real attached add-ons
• stakeholder demos before merging

Operational advice

Review apps are real environments that cost real resources. A few rules of thumb:

• pick small plans for review-app add-ons (postgresql:hobby-0, valkey:hobby-0) — they don’t need production sizing
• don’t bake long-lived production secrets into app.json. Set those out-of-band on the parent app.
• use pr-predestroy for any cleanup that needs to happen before the environment goes away (notifying systems, archiving logs)